Air purification filters frequently appear in the form of cartridges containing a metallic framework, generally having parallelopiped contours, on which a filtration means is attached.
Conventionally, such a filtering means may consist of a honeycomb filtration unit structure according to which a single semi-rigid membrane of a filtration material is shaped by folding in such a manner as to present a large number of juxtaposed filtration pockets.
However, such a known cartidge filter presents a certain number of disadvantages. In particular, the numerous folds and corners produced during the shaping of the honeycomb constitute traps for the dust or other particles extracted from the air. Thus, when the filter is cleaned, such as by reversal of the air flux passing through the filter and recovery of the dust separated from the membrane, the clogging of certain regions is such that the cleaning of the filter in these regions turns out to be impossible.
A second disadvantage of the known honeycombed cartridge filters lies in the fact that deterioration of the filtering material necessitates the replacement of the entire cartridge. This solution obviously is even more costly as the price of the filtration material increases.
Finally, the honeycomb structures, which require special shaping machines, add to the overall resale cost of such cartridge filters.
There is further known, e.g. from Swiss patent No. 255 947, U.S. Pat. No. 3,475,884 and European Patent No. 0 219 554 a filtering device wherein a plurality of filtration pouches are fixed removably to a plate or the like having a pluarality of openings for said pouches and fixed inside the filtering device.
Although good filtration efficiency may be attained with such device, it suffers from various drawbacks. First of all, the removal of a filtration pouch is difficult since it is necessary to operate inside the filtering device. There is also a risk in such operation that the clean side of the device gets polluted because of dirt separating from the pouch on which it has built up. Finally, such known structures need complicated holding arrangements at the closed end of the pouches, in order to keep them in parallel, spaced-apart relationship. Such holding arrangements make the dismounting of a pouch still more difficult.